G7 PSU Help Needed

[Guest]

If you have 68V at the anode your tube is drawing about 0.62mA. This is not too bad. Check the voltage at the cathode (K) pin 3 to verify this.

With power off, check resistance on the LL1538. Between pins 5 and 6 should be about 880ohms. Pins 1 and 2 should read 44 as should pins 3 and 4. There should be open between all other pin combinations and pin 6 is grounded. Not to be too confusing, but you could connect the pins 2 and 3, and pins 1 and 4 like the data sheet and have less chance to pick up noise. Just connect the traces where they are cut on the board.

If this measures OK lets see what we can do to find sound. Are you sure the speaker you are plugging into is OK? Try to measure AC at pins out + and out - while you make noise into the mike like clapping or something.

Try the above and let us know what you get.

 

[zebra50]

And check your cable. Have you used good screened cable? check all your connections and continuity there. It's easy it cross a couple of wires.

Please try to borrow a camera and post some pictures - it will be a lot easier to look for mistakes.

 

[reggie]

I will take some pics with a borrowed camcorder later and post them.

I checked the voltage at the cathode(pin3), I get about 1V.

Then I checked the Lundahl (I also downloaded the data sheet). I´m getting 25 ohms between 1/2 and 3/4 and 830ohms between 5/6. I also got 0.1ohms between 2/3 and 1/4 (I am using the pcb from gustav, which has connections there, but so tiny I´m not sure if they´re connected or not). So now I made connections between 2/3 and 1/4 (as I could also read from the data sheet), now I´m getting 0ohms.

My speaker/mixer hookup is ok, when I connect another mike it works fine.

I can now see on the meter of my mixer that there must be a VERY faint signal when I´m clapping, speaking, etc. Also I can measure 0.1V AC between pins out+ and out- when making noise.

I will check the cables again too (for wiring inside I just use a "normal" cable from the electronic supply).

thanks,
reggie

 

[reggie]

I took some pics now, excuse me for the bad quality, I just have a camcorder with a photo function here.
You can see them here:

http://www.3dmedicalanimation.com/downloads.html

now I just measured the lundahl with power turned off and I get resistance (0 V) between almost all of the primary and secondary pins. Not sure if this is supposed to be like that.

I also triple-checked all the wires and could measure signals going through everywhere.

 

[Guest]

With power off you should get 0V everywhere. Some general tips on soldering, try to use a small a tip and just enough heat to do the job and just a little solder. Leads should be short and components should be close to the boards.

Use your ohm meter to look for shorts between connections in the cable, each pin to every other pin. Then check your mike board for shorts as well. Get rid of any extra flecks of solder that have splashed on the board. With sensitive electronics housekeeping is particularly important to keep out stray noise.

Your transformer and tube look OK. I think your signal is being shunted away by a short/ground.

 

[reggie]

thanks a lot again for advice!

I know there´s some "ugly" soldering, it was a bit tricky with little space there. Some of it is due to the fact that I took parts in and out for checking stuff.

I went through all the cables and most other parts with the ohm meter already but maybe I still overlooked something.
Strange, I still get some resistance with power off between the primary and secondary of the lundahl.

I think my last resort will be now to just take off everything from the mic pcb and then clean it. Maybe it´s still usable afterwards, otherwise I will have to etch a new one myself ;-(

I´ll let you know, if I ever get the mic to work ...

thanks,
reggie

 

[Guest]

You should read open between any primary pin and any secondary pin with your ohm meter. If you are not, then there is a problem with that part of the circuit. Could be transformer or the board.

 

[reggie]

now I just finished taking off everything from the mic pcb, cleaning it and resoldering every part. I really did it very very carefully, took me 1 day.

but I rechecked the lundahl again and I definetely do NOT get an infinity measure between any primary pin and any secondary pin with power off! (I always get either zero or some other value). So if it´s like that, it must be that the lundahl is broken !?!
Could I have destroyed it or can it be, that sometimes they are defective from the beginning?
That would be a very very bad thing, cost me 60 ? ;-(((

 

[gyraf]

Is that measured mounted on the PCB, or when it is not soldered in?

If it is shorted when out of the circuit, I would try contacting Per Lundahl to see if I could get a replacement - they are very interested in keeping quality control at max, and internally shorted pri/sec is probably a thing they would want to have a closer look at.

Their email adress is at their website.

btw: I have never had one single LL-transformer failing - ever!

Jakob E.

 

[reggie]

It is when the lundahl is mounted on the PCB.
I did not take it out, because that is quite hard to do with those seven solderpoints.

So in the circuit, getting those measures is still ok? That sounds like good news, that they´re usually do not fail. I was just afraid, that I destroyed something maybe.

 

[gyraf]

I can't say how the transformer should measure in-circuit, but if you remove the output connections as well as the optional feedback trimmer and associated cap, you should have the transformer primary floating free, and hence no connection to ground (see and check the schematic). If you have ground connection still, and you've checked the PCB, you'll need to unsolder the transformer to verify if it's OK. Take care when unmounting the transformer, the pins rips out easily from the housing, breaking the internal wires.

Jakob E.

 

[reggie]

thanks for the info!
I think I will just very carefully take out the transformer (because I already soldered/de-soldered the other parts a couple of times and the pcb doesn´t get better if I do it again ..).
btw, I do not have the optional feedback trimmer and associated cap (as they are optional).

I also checked and re-soldered the psu pcb and wires again, just to be 100% sure ...didn´t change anything.

maybe I have a bad tube? I does get warm though, but I can´t see any glowing. I remember from my guitar amps that I had bad tubes once in a while, even taking a new one out of the package ... I just don´t know how I could check the tube.

 

[Brizco]

hello

i have the same problems: i use a 220v/ with 2* 15v and a 220v/ 2* 9v transformator

the 9v trafo works perfect, but on the end of the 15v trafo there is no voltage!

but when i test the 15v trafo with a 220v input there are exact 15v... so it cant be damaged, right?

do i have them wired right?

220V/9V 15V/220V

pri sec1/2 sec1/2 pri
___ ___ _____ ____
___ ______ ____

___ _______ ___
___ ___ ____ ____


thank you for your help!!

 

[ward]

Hi Brizco,

Your transformers appear to be fine.
Look at the datasheets of your transformers to check your using the right pins.

There's a good drawing by Zebra50 on how to hook them up on the first page of this thread, have you seen it ?

I don't understand your drawing sorry.

 

[Brizco]

thank you ward for your answer!

i solved the problem already! everything is okay now.

thank you!

 

[Dr-Mbogo]

Hi there,

i just finished everything... all but the housing (let's see what skylar will provide...)
Its about the psu. Everything including the voltages is fine. I use a lorlin for the pattern switch. In the meantime I destroyed about 3 of them. Whenever I switch there comes a noise out of the switch. It sounds just like there is a short inside. I opened the switch and there was a burned contact. What is wrong here? I am not sure what contact behaviour I should use. Make before break or the other way round? Or should I have a look at a something completely different part of the psu?

Merry Christmas to everyone who is around!

Chris.

 

[ward]

You need a break-before-make switch.
And I'd use something sturdier for the pattern switch.

 

[Dr-Mbogo]

Thanks for the quick response! Any recommendations for a more sturdy one?

 

[gyraf]

you can get Lorlin's in BBM-versions...

But I have never had this problem in any G7 pattern switch - have you modded the circuit, with e.g. an extra post-switch capacitor? That would severely disturb the switch. The circuit as-is (with two 100K resistors from HT, and going into a 10K at the microphone end) should NOT need too much consideration about MBB or BBM switches.

If you want additional pattern-voltage filtering, add it in the microphone (but you probably won't gain much benefit from this)

Jakob E.

 

[Dr-Mbogo]

thanks for the reply jakob,

there is no modification at all in the psu. I will try with a BBM Lorlin Switch. (Just ordered)

Chris